Ultrafast supercapacitors based on boron-doped Ketjen black and aqueous electrolytes

Compact supercapacitors (SCs) are considered as a promising alternative to bulky aluminum electrolytic capacitors (AECs) for alternating current (AC) line filtering applications. Although the recently-developed SCs based on heteroatom-doped and/or macro/mesoporous carbon materials exhibit sufficiently fast response speeds for such applications, improvements in their performance characteristics (e.g., capacitance) would be highly desirable. In particular, the SCs with heteroatom-doped carbons have thus far exhibited limited capacitances at high frequencies (<0.5 mF cm⁻² at 120 Hz). In the present work, SCs with boron (B)-doped mesoporous Ketjen black (KB) and a 6 M KOH electrolyte are shown to exhibit a high areal capacitance of 1.67 mF cm⁻², along with a high frequency response (negative phase angle, −Φ = 81.5°) at 120 Hz. The excellent performance of the B-doped KB SCs can be attributed to the improved wettability and electrical conductivity, and to the increased number of capacitive sites due to the B-doping. This demonstration may greatly contribute to the development of high performance SCs suitable for high frequency applications.